Improved cost effective and productive methods are constantly being sought to increase the production of hydrocarbons from hydrocarbon-bearing formations. Recently, water-superabsorbent polymers have been reported for use in gelled fluids as thermal insulating fluids. Such fluids, when added either into an annulus or riser, effectively reduce undesired heat loss from the production tubing, or heat transfer to outer annuli. In some cases, heat loss from the produced fluids due to conduction and convection can be reduced by more than 90% when compared with conventional packer fluids. Such fluids exhibit low thermal conductivity and are capable of securing the insulation of the wellbore while reducing the amount of heat transfer from the production tubing to the surrounding wellbore, internal annuli, and riser. Alternative materials, especially those that are environmental friendly, such as biodegradable additives, have been sought as well as insulating compositions which are oil based.
In addition to their use in thermal insulating compositions, gelled fluids, such as oil or hydrocarbon based gels, have been used for other oilfield applications, such as hydraulic fracturing, acid stimulation, drilling, drill-in, and fluid loss control fluids. In particular, such liquids have been used in drilling applications as synthetic oil based drilling muds.
Gelled organic liquids, such as hydrocarbons, are typically prepared by introducing into the organic liquid (or hydrocarbon) a phosphate ester based gelling agent and an aluminum-containing or ferric-containing crosslinking agent or activator. The reaction between the phosphate ester and aluminum or ferric crosslinking agent forms an aluminum phosphate ester or ferric ester which, in turn, gels the organic liquid. Alternatively, organic liquids may be gelled by introducing a phosphate ester into the organic liquid (or hydrocarbon) and then reacting the liquid mixture in-situ with a metal activator.
In hydraulic fracturing, the viscosity of the fluid must be sufficiently high as to suspend and carry the proppant as it enters the formation but sufficiently low to be readily pumpable. The viscosity of the gel must further be sufficient to prevent the proppant from prematurely settling from the gel. If the gel is overly viscous, pumping becomes difficult. In such instances, delayed gelling is desired.
Delay gelling can reduce the friction of the fluid while it is being pumped downhole through the production tubing. This further may reduce the required pumping horsepower. Delayed gelling may also reduce the negative impact of shear on fluid properties. Depending on the pumping rate and tubing size, the desired delay time of gelling can vary from minutes to hours.
In other applications, such as when the composition is being used as an insulating fluid, delay gelling is required due to the limited access to the annulus during the placement of the fluid into the annulus. The desired delay time of gelling in such situations is usually much longer, typically ranging from hours to days.
Oil based gels are usually required when the hydrocarbon-bearing formation is sensitive to water based fluids. Several methods have been used to delay gelling oil-based gels. Such methods involve the addition of chelating agents to an aqueous aluminum-containing activator to control the availability of active aluminum ions. This approach, however, typically delays gelling for only a few minutes. Alternatives have been consistently sought for oil-based gels which exhibit delay gelling for longer periods of time.